04-02-2017, 04:23 PM
Hi Doug,
Thankyou for the two very helpful links. I have studied both. Assuming that Philips knew what they were doing when they developed a kit for convering the FM828 into a TTR, and I'm sure they did, the first link would indeed give me guidance on the best way to route the audio from RX to TX. I will probably need to look at the instructions with a circuit diagram and a radio in front of me in order to understand it fully.
The first link does not really address the RX tuning issue, but the second does. Indeed, the first link suggests that U-band radios were designed for 440-470 MHz, from which one might infer that there would not be too much difficulty in tuning for 438-440 MHz repeater use, noting of course that the input frequency is 5 MHz lower. Information in the second link indicates that U-band radios were designed for 450-470 MHz, and they need an extra half-turn turn added to the front-end helical filters, which accords much more with our experience building a repeater in Sydney. However, when we add a half turn to the helical filters, although they all peak quite convincingly at 434-435 MHz, we do not get the sensitivity that we would expect.
On the basis of this, I think there is another issue, and I will address that in another post under the heading of FM, Repeaters, D-STAR when I get time.
In the meantime, I wonder if there is anyone else out there who has anything to contribute on this subject? Does anyone know of a document produced by a VK5 group?
Best wishes,
Lew.
Thankyou for the two very helpful links. I have studied both. Assuming that Philips knew what they were doing when they developed a kit for convering the FM828 into a TTR, and I'm sure they did, the first link would indeed give me guidance on the best way to route the audio from RX to TX. I will probably need to look at the instructions with a circuit diagram and a radio in front of me in order to understand it fully.
The first link does not really address the RX tuning issue, but the second does. Indeed, the first link suggests that U-band radios were designed for 440-470 MHz, from which one might infer that there would not be too much difficulty in tuning for 438-440 MHz repeater use, noting of course that the input frequency is 5 MHz lower. Information in the second link indicates that U-band radios were designed for 450-470 MHz, and they need an extra half-turn turn added to the front-end helical filters, which accords much more with our experience building a repeater in Sydney. However, when we add a half turn to the helical filters, although they all peak quite convincingly at 434-435 MHz, we do not get the sensitivity that we would expect.
On the basis of this, I think there is another issue, and I will address that in another post under the heading of FM, Repeaters, D-STAR when I get time.
In the meantime, I wonder if there is anyone else out there who has anything to contribute on this subject? Does anyone know of a document produced by a VK5 group?
Best wishes,
Lew.